1. Field of the Invention
The present invention relates to a process for producing a cement building material.
2. Description of Related Art
In the construction and building industry concrete is generally defined as a mixture of two components, aggregates and paste. The paste, which typically includes Portland cement and water, binds the aggregates (sand and gravel or crushed stone) into a rocklike mass as the paste hardens. The paste hardens because of the chemical hydration reaction between cement and water. In this regard, the technology of concrete is discussed in S. H. Kosmatka and W. C. Panarese, "Design and Control of Concrete Mixtures," 13th edition, Portland Cement Association, 1988.
The paste component of concrete, either separate from or combined with aggregate, forms a relatively continuous and consistent solid when cured. In conventional cured paste, voids or small discontinuities are normally found which have a deleterious affect on the performance characteristics of the cured paste and concrete. Commonly such limitations on performance characteristics include failure under heavy load and stress conditions.
The most common constituent of the bonding material in the concrete, i.e., that which bonds the aggregate, is Portland cement paste. The four principal chemical constituents of Portland cement are tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite. These components react with water (hydration) causing the setting and hardening of the cement. The process of cement hydration is characterized by the formation of a polymorphic crystalline mass as discussed below.
Studies have found that the constituents of Portland cement experience generally constituent specific partial hydration when processed by conventional means. This results in characteristic polymorphic crystalline formations of calcium silicate hydrate and calcium sulfoaluminate "ettringite" (exemplified by a needle-like structure), calcium hydroxide "Portlandite" (characterized by hexagonal crystalline plates), a spindle columnar crystal structure and an amorphous calcium silicate crystal structure. Colonies of these polymorphic crystalline mass formations are observed in random disposition relative to each other within typical cured cement pastes. This visually observably dissimilar crystallization has long been accepted and attributed to the chemical reaction between water and the tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite components.
One apparatus patent of particular interest to the process of the present invention is U.S. Pat. No. 4,552,463. This patent discloses an apparatus shown generally in FIG. 14 comprising a hollow enclosure (12') having a feed inlet (14') to receive water and Portland cement to be colloidalized into a paste, and a discharge outlet (16') to dispense the colloidal paste. A rotatable drive shaft (38') is disposed along the central longitudinal axis of the enclosure. Several flat baffles (68') and (74'), disposed in planes parallel with the shaft (38'), extend from the inner walls (76') and (78'), respectively, of the enclosure (12') towards the shaft (38').
Connected to the shaft (38') is a first upper set of downthrust blades (26') which are substantially horizontal and which thrust the mixing water and cement downward in direction "a", a second upper set of downthrust blades (28') substantially perpendicular to the first upper set of downthrust blades (26') which direct the mixing water and Portland cement inward towards the drive shaft (38') in direction "b", a lower set of down thrust blades (30') which thrust the mixing water and Portland cement downwardly and outwardly in the direction "d", a lower set of horizontal upthrust blades (34') which thrust the mixing water and Portland cement upward in direction "e" between the baffles (68') and (74'), and an upper set of upthrust blades (32'). These blades (32') are horizontal to the first upper set of downthrust blades (26') and perpendicular to the second upper set of downthrust blades (28'). In general they thrust the mixing cement and water upward in direction "e". As can be seen in the figure, the upper and lower baffles are spaced apart to create a space for receiving the upper set of upthrust blades (32').
Although the apparatus disclosed in U.S. Pat. No. 4,552,463 provides a superior paste, there is a continuing need to improve upon the paste and in particular to improve the strength and performance of the building material resulting from curing paste by conventional curing techniques. It is to this object that the process of the present invention is directed.